Treatment of nickel cathodes



Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE TREATMENT OF NICKEL CATHODES No Drawing. Application January 9, 1936, Serial No. 58,322

3 Claims. (01. 148--19.9)

The present invention relates to the treatment of nickel cathodes obtained by electrolytic deposition and has for its object certain improvements in the method of treating the electrolytically deposited cathodes whereby their solubility characteristics particularly are so greatly improved that the cathodes may be directly used as anodes in nickel plating baths.

It is well known that nickel cathodes obtained by the usual electrolytic deposition processes are so poorly soluble that they are not suited as anodes in the nickel plating industry. Nickel anodes as ordinarily made are either cast directly into finished anodes, or are cast into slabs which are then mechanically worked, as by rolling, possibly followed by annealing, and then cut into proper shapes. This is an expensive procedure. It has been proposed (see for example L. D. Hammond, Trans-Amer. Electro-chem. Soc. 1921, 39, 483) to anneal nickel, in electrolytic furnaces, to increase its solubility so that it may be used as anodes. In addition to the high cost of these furnaces and their operation, a number of troublesome difficulties are met in attempting to produce soluble nickel anodes by annealing electrolytically deposited nickel cathodes. tain factors are encountered that materially affect the quality of the final product. and uncontrollable heating, as well as oxidation of the cathode plates by the action of air, the formation of oxides andthe like on the plate surface, may substantially reduce the mechanical strength of the cathode plates in part or whole. The cathode plates may not be rendered sufficiently and uniformly soluble. They may have a highly tarnished surface. The treated nickel cathodes may be of such. poor quality as to cause an increased amount of scrap and .slimes on use as anodes, etc. As a result of these difficulties,

it may be necessary to subject the nickel cathodes to a subsequent treatment step or steps, such as a careful cleaning of the plate surfaces, before they may be used as anodes in the nickel plating industry.

In accordance with the present invention, these difficulties are readily and economically overcome. Electrolytically deposited nickel cathodes are treated in such a manner as to improve greatly their solubility characteristics. They are caused to have clean and bright metallic surfaces. The plates are substantially uniform in quality.

In the practice of the invention the cathode plates are heated in a molten salt bath consisting of a salt or salts of such a character as not Cer- Uneven .cathodes should not be in contact with anythenuquenched in water.

to attack the metallic nickel under the prevailing conditions, with or without the addition of substances capable of dissolving oxides or the like which may be present on the surface of the nickel plates. When the cathodes, which are rela- 5 tively cold compared with the molten bath of salts, are first immersed in the salt bath, a layer of the salt solidifies on the cathode surfaces. In order to obtain the solubility characteristics desired, the cathodes must be permitted to soak in the salt bath, and thus continue to be heated, until the layer of solidified salt on the cathodes is dissolved or melted. The time required to obtain this effect depends on the initial and continued temperature of the salt bath. In a preferred practice, heat is continuously supplied to the salt melt to keep it at a substantially uniform temperature.

A suitable salt melt may for example consist of sodium chloride, NaCl, or potassium chloride, KCl, or a mixture of these salts, if desired, with the addition of borax or like substances capable of dissolving oxides that accumulate on the oathodes.

When the nickel cathode plates are placed in the molten salt bath for heating, care should be taken to avoid direct contact between adjacent plates or between the plates and other objects,

such as the sides of the vessel containing the molten bath, because such contacts tend to disturb the uniform heating and hence the ultimate solubility characteristics of the plates. It is therefore desirable that the broad faces of the thing except the molten salt bath.

After the heat treatment, the plates .are removed while in a'red hot condition. They are If the plates areoirectly transferred from the bath of molten salt to the quenching water, they tend to tarnish at 40 the surface. This is probably due to the formation of steam at the surface of the cathodes when they are submerged in the water. When the plates are removed from the molten salt bath, a coating of the salt adheres to the surface. When the cathodes are first submerged in the water, the adhering coating of salt is promptly blown and washed off, so that the coating does not pre-' vent the steam from contacting the hot plates. The steam has a tarnishing effect on the hot. plates.

This slight tarnishing of the plates may be overcome by allowing the red hot plates, when removed from the molten salt bath, to cool for a minute or two until the red hot color vanishes,

and thereafter quenching the plates in the water. The plates are advantageously cooled in the open air until their red hot color disappears. During this cooling down step, the adhering coating of salt protects the plates against oxidation by surrounding air. The coating rapidly dissolves in the water employed for the quenching step. When the operation is carried out in this way, the cathodes are given a bright metallic surface without any special after-treatment.

The adhering coating of salt on the hot cathodes removed from the molten bath, as just noted, protects the cathodes from contact with surrounding air. There is thus no tendency for the nickel to become brittle or abnormally weakened owing to creeping oxidation between the crystals.

EXAMPLES Nickel plates obtained by electrolytic deposition are dried in the air and are then introduced into a bath of a molten mixture of NaCl and KCl having a temperature of about 800 C. The plates are kept in the bath out of Contact with one another at constant temperature for about a quarter of an hour, whereupon they are removed while red hot, and are then quenched in water in a tank of suitable size and form. A coating of salt adheres to the plates when they are transferred from the salt melt to the water, and prevents access of air to the surface of the hot plate so that oxidation is avoided.

The plate on being submerged in the water is rapidly cooled and at the same time the coating of salt is dissolved and removed. The plate so treated has a bright metallic surface and maybe sub-divided by shearing, and afterwards straightened and worked as usual.

Owing to the fact that the time during which the plates are submerged in the water for cooling is quite short, and because the cooling water will become gradually enriched in salt from the Electrolytically produced nickel plates having a. size of about 60 x 90 cm. and a thickness of about 6 mm. are heated in a salt bath of the same composition as specified in Example I, without being subjected to any preparatory treatment except drying in air. The salt melt is contained in an electrically heated vessel having a diameter of about 1 m. and a height of about 1 m. One nickel plate at a time is lowered into the melt by means of a tackle and is maintained hanging in the bath for about 5 minutes. It is then hoisted into the air and permitted to cool for a minute or two, until its red hot color disappears, after which it is dropped into a quenching bath. The cooled plates from the quenching bath are set aside until dry. The percentage of alkaline metal chlorides in the nickel of the plates is about 0.002 per cent (KCl-i-NaCl) The plates are employed as anodes in the plating bath without any further treatment.

This application is a continuation-in-part of my application, Serial No. 685,223, filed August 15, 1933.

I claim:

1. In the method of treating electrolytically deposited nickel cathodes to make them more readily soluble when employed as anodes in the nickel plating art, the improvement which comprises immersing the cathodes in a bath of molten salts maintained at a substantially elevated temperature, soaking the immersed cathodes in the bath of molten salts sufficiently long to dissolve the layer of solidified salt that forms on the cathodes when they are first immersed and to cause the cathodes to become red hot, removing the oathodes from the bath, and quenching the cathodes while still hot in water, a coating of the salt from the molten bath being maintained on the oathodes during their transfer from the saltbath to the water whereby access of air to and oxidation of the surface of the hot cathodes are prevented.

In the method of treating electrolytically deposited nickel cathodes to make them more readily soluble when employed as anodes in the nickel plating art, the improvement which comprises im ersing the cathodes in a bath of molten salts mai tained at a substantially uniform elevated temperature, keeping the broad faces of the cathodes so immersed substantially out of contact with surrounding objects, soaking the immersed cathodes in the bath of molten salts sufficiently long to dissolve the layer of solidified salt that forms on the cathodes when they are first immersed and to cause the cathodes to become red hot, removing the cathodes from the bath, and quenching the cathodes while still hot in water, a coating of the salt from the molten bath being maintained on the cathodes during their transfer from the salt bath to the water whereby access of air to and oxidation of the surface of the hot cathodes are prevented.

3. The method according to claim 2, in which the red hot cathodes removed from the bath of molten salts are permitted to cool in the open air until the red color disappears before they are quenched in the water.

ANTON MARTIN GRONNINGSAETER. 

